Method of planing helical teeth, more particularly for bevel gears



H. BRANDENBERGER. 7 METHOD OF PLANING HELICAL TEETH, MORE PARTICULARLY FOR BEVEL GEARS.

APPLICATION FILED JAN. 5. 1921.

Patented Nov 28, 1922.

4 SHEETSSHEET I.

. H. BRANDENBERGER.

METHOD OF PLANING HELIGAL TEETH, MORE PARTICULARLY FOR BEVEL GEARS.

APPLICATION FILED JAN- 5. I921.

mswssa Patented Nov. 28, 1922.

4 SHEETS-SHEET 2.

H. BRANDENBERGER. METHOD OF PLANING HELICAL TEETH, MORE PARTICULARLY FOR BEVEL GEARS.

APPLICATION FILED JAN: 5. 1921. 1,436,938.

Pat ented Nov. 28, 1922.

4 SHEETS'SHEET 3.

APPLICATION FILED JAN-5,1921.

. mama Patented Nov. 2%, 1922.

4 SHEETSSHEET 4.

Patented Nov. 23, 1922..

that

METHOD OF PLANING HELICAL TEETH, MORE PARTIGULAELY FOR BEVEL GEARS.

Application filed January 5, 1921. Serial No. 435,267.

To all whom it may concern:

Be it known that I, Hniivnrorr Britannica nnrcnn, a subject of the Republic of Switzerland, residing at 10 Degengasse, Vienna Xvi, Austria, have invented. certain new and useful Improvements in Methods of Planing H lical Teeth, More Particularly tor Bevel Gears (for which I have filed applications in Austria, May 2, 1919; Gen man June 26, 1919; France, Aug. l, 1920; Fh-veden, June 26, 1920; Switzerland, Sept. 7, i920; Italy, Sept. 17, 1920), of which the following is a specification.

it is known to form helical teeth on bevel wheels by planing in the manner, whereby the bevel blank (work) rotates. while the cutting tool moves towards the cone apex. The line of cut thereby resulting is a relative movement of the cutting tool to the bevel blank.

The subject of the present invention comprises a method of planing accurate helical teeth on bevel gear wheels, in which the tooth works towards the cone apex in a known manner and the blank is rotated at the same time, wherein the tool, however acts in a novel manner such that its cutting edge is inclined to its line of cut and exactly or approximately perpendicular to the straight lines on the pitch plane along which the tool moves towards the cone apex.

In the case of the hitherto known methods of generating helical teeth on bevel wheels this definite arrangement of the tool was not obtained but the tool was set by being simply rotated about itself into an apparently suitable position.

With the arrangement of the cutting edge of the tool according to this invention, such a setting will not suflice because for a definite involute angle with the same possibility of adjustment the tool, must previously be ground in a definite manner and then again the tool must be brought into a precise position. The advantage of setting the tool in accordance with the invention consists in this, that the flank of the bevel wheel situated in a plane perpendicular to the generator is cut with the self-same disposition of the cutting edge 13 of the tool during the rolling off of the cone upon the crown wheel.

Figures 1 to 4 illustrate the general formation of the tooth.

Figure 1 shows a crown wheel with straight teeth.

Fig. 2 shows the same tooth generated with different angular positions of the edge of the tooth.

Fig. 3 shows tooth 01" a crown wheel having spiral teeth.

Fig. 4 shows the same tooth formed from the number of straight lines.

Figs. 5 to 9 illustrate the generating principle according to the present method in which the work-piece etc. is rolled off.

Fig. 5 shows the tooth of a bevel wheel with spiral teeth.

Fig. 6 is a similar view in which the edge oi the tool is inclined. l

Figs. 7 and 8 are an elevation and of a prismatic tool.

Fig.9 is a section along 2 in Fig. 7.

Fig. 10 shows the absolute movement of the edge of the tool, the upper portion of the view being an elevation and the lower portion of the figure being a plan view showing the absolute movement and also the relative movement of the edge of the tool.

Fig. 11 shows the profile oil' the tooth and the line of contact of a wheel capable of gearing with any one of the set of interchangeable gear wheels.

Fig. 12 shows the tooth of a wheel which is not capable of gearing with any number of interchangeable gear wheels.

Fig. 13 shows the profile of two teeth in engagement with one another together with their lines of contact which. however does not coincide. I

Fig. 14. shows the tooth profile of a crown wheel together with the line of contact for two bevel wheels which are capable of mesh ing withone another.

Fig. 15 is a perspective view showing the relativemovement of the cutting tool relatively to the crown wheel.

Fig.16 is a perspective view showing the relative path of the tool corresponding to the plan and elevation shown in Fig. 10.

When producing bevel gear wheels with straight teeth, the working edge of the tool describes a plane, the surface 1 of the crown wheel 2 (Fig. 1 of the drawings) it being immaterial, which of the straight lines 3 or 4 of this surface (Fig. 2) is made to constitute the edge of the tool.

When forming helical teeth on bevel gear wheels by planing (Fig 3), the positions (3, 4 in Fig. 2) of the working edge of the plan 70 tool with reference to the crown wheel 2,

imagined to rotate with the bevel wheel, are no longer parallel to one another (Fig. l), but, with the straight lines drawn from corresponding points of the momentary tool positions, for instance from the points X on the pitch surface, to the cone apex S, enclose equal angles a, because the edge of the .tool comes into action at different positions of the rotating crown wheel during the movement of the tool towards the cone apex. The flanks of the teeth ofthe crown wheel will be made up of straight lines if the cut-' ting edge of the tool happens to be straight. T he pitch plane of the crown wheel touches the pitch cone of the work and rotates with the work. The cutting edge of the tool (assumed to be a straight line in Fig. 10) moves from the position Ma a to the position Mb b in such a manner, that the point of the tool moves towards the cone apex S from Me to MY), while the crown wheel (and with it the bevel blank, which is imagined to be in gear with the crown wheel) rotates about the angle Ma S Ma. The point Ma of the tool thereby describes a groove Ma MT) upon the crown wheel, while the cuttin edge Ma a of the tool enerates a surface a Ma Mb Z). This b tooth surface (4 Ma Mb 2') of the crown wheel will be composed of straight l nes as the cutting edge Ma-a of the tool is straight.

The point Ma of the tool moves along the root of the tooth towards the cone apex. The actual edge Ma-a of the tool describes a plane, which likewise passes through the cone apex, so that the edge of the tool moves towards the cone ape): at the pitch surface along the straight line Ta T7). The tool accordingly rises out of the body of the cone, whereby the tooth spaces become proportionately smaller towards the cone apex.

If a sphere be described about the apex S as centre and mace to intersect with the flank of the tooth, of the crown wheel for instance, then a curve will be obtained, the tangent of which on the pitch surface will enclose with the latter an angle, which will he called the inrolute angle and which must be equal to the corresponding angle of the mating wheel, therefore predetermined in the case of the mating wheel. For every predetermined involute angle at the pitch circle, a suitable straight line in the plane 15 (Fig. 3) tangential to the warped tooth surface can be selected as cutting edge.

iccording to the invention, an entirely definite position of the cutting edge of the tool is selected from the many arrangements possible.

If two bevel gear wheels in. engagement be made to intersect with a sphere, the

centre of which is laid on they joint cone apex, then, with the tooth surfacesas intersection, tooth flanks are obtained which roll esseee or slide off from each other during the period of contact. The locus of the successive points of contact of these tooth-profiles is called the line of contact (line on which contact takes place).

If a theoretically correct contact takes )lace, then the largest spherical segment inersectii. the instantaneous point of contact and perpendicular to the tooth flank at the cor esponding point, must pass through the insnntaneous point of contact of the pitch circles. From this it follows, that the line of contzut is independent of the mating wheel. must be the same for both wheels low 1' and so disposed, that they will coincide when the wheels are brought into engement. If the line of contact is ce n- "nnnetr1cal with respect to the point L pitch circle throu...1 whichv it passes,

of the p then the wheels have the pmperty of intereability, that is to say, all wheels which hare these lines of contact can he made to gear with one another and consequently h one and the same crown wheel as well. the li es of contact of the face and root he ('liilere'ntly constituted, then two wheels (wheels which are capable of together) can no longer be produced single crown wheel but only from we crown wheels, which have substituted lines of contact relative to the face and 3, 18 in Fi 11 he a tooth flank the characteri. ie of interchangeable reels, then is line of contact 19, 1'7, nated ccn ll symmetrical relative H that is to say., a point 21 of "act corresponds to a point 22 e so that 21, 17, 22 is a and 17 the bisecting point. a tooth flank is shown, where- 2d, placed symmetrical to the point .23 rel tire to, 17, no longer lies upon the line of contact 21, 17, 20.

If new two wheels, which are produced from the self-same crown wheel having an unsymmetrical line of contact. be put into ear, they will not coincide. In Fig. 13, 25

and 26 are tooth flanks, 27 and 28 the lines lent to theline of contact of the root flank of the other wheel, the functions of the face and root flanks of the crown wheel will have to be substituted.

Such crown. wheel is shown in Fig. 14;. 31, 82, 33 is the line of contact of the tooth flank 34, 85. One of the bevel wheels must be capable of being rolled off with the crown wheel in gear on the side A thereof, the mating wheel for it being capable of rolling off with the same crown wheel but on the side 13.

These investigations, up to now of a general nature, hold good for bevel gear wheels as well as spur wheels, in which the centre of the sphere extends back to infinity.

Now helical bevel gears have a line of con tact, which does not lie centrally symmetrical with respect to the sphere, because one wheel has a left handed spiral, the other wheel a right-handed spiral. in the present method, the generation of the spiral is effected in such a manner that the cutting tool moves towards the cone apex in ac cordance with a definite cont nually recurring law, while at the same time, the work (bevel blank) rotates about its axis, again in conformity with a definite law (for instance uniformly), the generation of the right or left handed spirals of two wheels running in engagement with one another being caused by reversing the directionof motion of the work (bevel blank).

It is immaterial for the purposes of the invention, in what manner the cutting tool arrives again in the same tooth space; this can be effected either by reverse rotation or continued rotation of the bevel blank.

In what follows, the work (bevel wheels) will not be further investigated but onlythe crown wheels, which result from the motion of the tool and with which the bevel wheels may be imagined to be in gear. The crown wheel takes part in the rotary motion of the work, in such a manner that the pitch plane of the crown wheel which touches the pitch cone of the work, has the same peripheral velocity as the latter (rotates continuously with it). The cutting edge of the tool generates upon the rotating crown wheel a surface, along which it always moves again afresh. Besides the contact movement an additional rolling off s required during the rotation for generating the shape of the tooth flank, so that the contact of the crown wheel with the bevel wheel (work) is effected at relatively different places. In order to effect this, all the hitherto known rolling-off mechanisms on bevel gear cutting machines can be utilized.

The feature of the invention consists in selecting the tool position in such a manner, that the crown wheels for the left and righthanded wheels will satisfy the above-mentioned requirements, namely that both are identical to each other, if the one is viewed from above, the other from below, so that during the cut, the self-same crown wheel comes into action only differently-handed.

In Fig. 15, p 9 denotes the stroke of the tool, angle 79 S the simultaneous rotation of the crown wheel and work respectively, p g the relative path of the tool upon the crown wheel (or work).

In Fig. 15, moreover p, g, is the movement of the point of the cutting tool towards the cone apex, p 30,, g, g the relative path of this point over the rotating crown wheel, il 2 2 2 2 1. P1 P1", 91 11 Q1 and Q 9 represent the relative positions of the cutting edge of the tool with respect to this crown wheel.

the tooth surface of the crown wheel; )7 p, (1, (l is the intersection with its pitch plane. p p, 9 represent those points of the tool positions, which are the same distance from the crown wheel plane as the corresponding points 19 p, g, If two wheels running in engagement with one another have to be cut, in which the deflendnm of one wheel is equal to the dedendum of the other, then 29, p, represents the relative path along which the point of the cutting tool-must. travel during the cutting of the mating wheel, whereby the ci'itting edge of the tool will have to sweep over the same tooth surface, in this case however from the other side. As this curve 2 7), g," will be produced simply by altering the direction of motion of the work and with the same law of motion for the cutting tool as for p p, q, 9', it follows that corresponding points as p, 22 must be reciprocally equal distances from the cone apex S. If this be the case, then 33,, which is equidistant from p, and 79 is the base point of the normals from the cone apex to the cutting edge of the tool and falls upon the pitch surface of the crown wheel. From this it will be seen, that with this method, the cutting edge 20, p, 79 of the tool extends perpendicular to the straight lines 2), S in the pitch plane, along which the tool moves towards the cone apex while the bevel wheel is rotated. It will be easily comprehended in what manner it will be necessary to proceed in the case of corrected gearing, in which the tooth height for both wheels is unequally divided between the face and root. The points of the tool cut at which the tool points lie successively will again have to be equi-distant from the apex of the bevel wheel.

The tool setting in consequence will also be effected in the case of unequal division of the tooth height, just as if standard teeth with equal depth of tooth for both wheels were being dealt with.

The tool cutting edge a is at its pitch point Ta perpendicular to the straight line Ta S, along which it moves towards the cone apex S. (:90), while it encloses with the pitch plane 2' of the crown wheel the angle e which is equal to the involute angle. If the tooth flank a Ma Mb 6 be made to intersect with a sphere with centre at S, then the tooth curve Z is obtained to which a is a tangent at the point Ta.

If the tool is not in the precise position, then a flank situated in a plane perpendicular to the generator is cut with different The surface represents mation into question, while with dispositions of the tool, because the straight lines 6, 7, S (Fig. 6), which are determined by the positions of the cutting edge of the tool, enclose with the straight line which passes through the cone apex S an angle differing from 90. With such a forof the tooth flanks, only an approximately suitable shape can come the cutting tool operating in accordance with this invention, the involute angle can be accurately adjusted because it is equal to the cutting tool angle, as well as the flank shape of these helical bevel gear wheels being quite as exact as in the case of bevel wheels with straight teeth.

Figures 7 and 8 illustrate an actual side tool with a cutting edge which operates in accordance the present method, in that the cutting edge 9 is inclined to its line of cut 10 and exactly or approximately perpendicular to the line of motion 11 of the tool, that is to say to the straight lines on the pitch plane oi the crown wheel, along which the tool moves towards the cone apex.

The tool is made of prismatic shape, in order to maintain it in serviceable condition simply by grinding the surface 12. In these figures, it is also shown that the edges of the prism besides the inclination Z to the crown wheel plane, have another inclination a to the line of motion of the tool, in order to obtain a clearance angle 3 to the line of out in a simple manner.

As the cutting point of the tool must move along a generator of the root cone, (that is the cone the surface of which passes through the base of the tooth)'in order to form the bottom of the tooth, then the straight line along which the point of the tool moves W111, with the pitch plane of the point of the tool by altering the angle I a. However, during the changing of this angle a, care must be taken that the clearance angle [3 (Fig. 9) remains greater than zero. For better comprehension, Fig. 9 shows the active portion of the tool illustrated in Figures 7 and 8 during the out.

What I claim is l. The method of cutting accurate helical teeth on bevel gear wheels by means of a tool working towards the apex of the rotating bevel blank, consisting in applying the tool so that its cutting edge is inclined to the line of cut and substantially perpendicular to the straight lines on the pitch plane,

along which the tool moves towards the cone.

apeX.

2. The method of cutting accurate helical teeth on bevel gear wheels as claimed in claim 1, wherein a tool of prismatic shape is used, the said tool being set at an angle to its line of motion.

In testimony whereof I have signed my name to this specification.

Ing. HEINRICH BRANDENBERGER.

Witnesses:

HUGO REIK, ANTON KUBIK. 

